The present invention relates to a portable remote terminal apparatus such as a portable telephone and the like and, in particular, to a portable remote terminal apparatus which can reduce the power consumption thereof.
FIG. 13 is a block diagram of the structure of an ordinary portable remote terminal apparatus according to the prior art. As shown in FIG. 13, the present conventional portable remote terminal apparatus comprises an antenna 71c used for communication with a base station, an RF section 72c which performs a high-frequency signal processing, a digital processing section 73c which performs a digital data processing, an operation section 74c including a push button and the like, and an audio section 75c including a microphone/speaker section and the like.
The digital processing section 73c includes a high-speed CPU (Central Processing Unit), while the digital processing section 73c not only executes digital data processings such as a speed signal encoding/decoding processing, a transmission line encoding/decoding processing, a TDMA timing control processing, a protocol processing, a clock control processing, and a man-machine I/F control processing, but also controls the whole of the present portable remote terminal apparatus.
In a portable remote terminal apparatus such as a portable telephone of a PHS type, a portable telephone of a PDC (Personal Digital Cellular) type and the like, normally, there is employed a TDMA (Time Division Multiple Access) system, in which a user communicates with a base station using a control channel, registers his or her own whereabouts, and responds to a call from the base station. However, in this type of portable remote terminal apparatus, normally, call-receiving from the base station is not successively executed but, for example, in the portable telephone of a PDC type, receiving is executed intermittently from the base station. And, in such intermittent receiving state, the user communicates with the base station in such a manner that receiving is executed at a rate of a receiving period of 6.6 ms (=1 slot) per call in up to thirty six subframes (one subframe=20 ms).
Conventionally, most of the portable remote terminal apparatuses employ a battery as their drive sources and thus it is desired that the power consumption thereof is as small as possible. As means for reducing the power consumption of the portable remote terminal apparatus, there has been employed a method in which, when the portable remote terminal apparatus is in a wait state and in an intermittent receiving state, the CPU of the portable remote terminal apparatus is set into a sleep mode to thereby stop the supply of a clock, or a method in which, in the above-mentioned case, the CPU of the portable remote terminal apparatus is set into a sleep mode to thereby lower the frequency of the clock.
Also, even when the CPU is set in the sleep mode, the CPU is returned to a normal mode at a given cycle in order to detect a call from the corresponding terminal apparatus thereof, and executes a detect operation to detect whether a keyboard is pressed down or not. If the keyboard is pressed down, then the CPU scans keys, recognizes and processes a key which is pressed down, and, after then, turns into the sleep mode again; that is, this series of operations are executed repeatedly.
However, in the above-mentioned conventional portable remote terminal apparatuses, as described above, since the CPU detects the key depressing even during the intermittent receiving period, the CPU returns from the sleep mode to the normal mode at a given cycle for scanning, which increases the power consumption of the portable remote terminal apparatus during such operation. Also, if the clock oscillator is stopped even during the intermittent reception, then there occurs an initial unstable period in the output when the oscillation is resumed, and it is difficult to match the clock oscillation to the timing of a receiving signal. In view of this, during the intermittent reception, although the clock supply to the CPU is being stopped, the operation of the oscillator is not stopped. This results in the increased power consumption of the clock oscillator.
Further, FIG. 6 is a block diagram of the structure of a portable remote terminal apparatus according to the prior art. Here, the portable remote terminal apparatus shown in FIG. 6 consists mainly of a communication function section and a data transmission function section: in particular, the communication function section is composed of an antenna 4b, an RF/IF section (high-frequency/intermediate-frequency section) 5b, a digital processing section 6b, an operation section 7b, an audio processing section 8b, a microphone/speaker 9b, and the like; and, the data transmission function section is composed of a UART (a start-stop synchronous data transmit-receive section) 1b, a high-frequency clock oscillator 2b for driving the UART 1b, an external interface 3b, and the like.
The digital processing section 6b comprises a high-speed CPU (central processing unit) 6b-2, a memory 6b-3, and a clock oscillator 6b-1 for a clock, and is structured such that it not only executes digital data processings such as an audio signal encoding/decoding processing, a protocol processing, a clock control processing, a control signal processing, but also controls the whole of the present portable remote terminal apparatus.
Also, when a transmission system is a start-stop synchronous system, a transmission speed (baud rate) is selected properly out of 600, 1200, 2400, 4800, 9600, 19200, 38400 bps according to the functions of lines or equipment used, while the accuracy of a sampling clock and a baud rate clock must be secured within .+-.1%, and, therefore, the UART 1b is structured such that it can be operated by an output signal of a 12.6 MHz high frequency output from the high-frequency clock oscillator 2b. Also, the external interface 3b is an interface which is used to connect the present portable remote terminal apparatus with an external device.
In the above-mentioned conventional portable remote terminal apparatus, as described above, during the intermittent receiving operation, the CPU 6b-2 is set into the sleep mode thereof to stop the supply of the operation clock or lower the frequency of the operation clock, thereby being able to reduce the current consumption of the CPU 6b-2. However, since the UART 1b uses the high-frequency clock oscillator 2b of 12.6 MHz regardless of the transmission speed (baud rate), the current consumption increases during the data transmission operation (because the current consumption is in proportion to the frequency used).
However, in the above-mentioned conventional portable remote terminal apparatus, even when the sleep mode (operation stop state) of the CPU continues for a long time in the intermittent receiving state, a clock oscillating source (an oscillator which oscillates a clock of high frequencies ranging from several MHz to several tens of MHz) is always held in the oscillating state, not only in order to match the clock oscillation to the timing of a receiving signal, but also because, once the clock oscillating source is stopped, when resuming the operation of the clock oscillating source, it takes time before the oscillation thereof is stabilized, which results in the wrong timing. Also, the present clock oscillating source requires the power consumption up to several mA and thus it wastefully consumes the power of a battery which is the drive power source of the portable remote terminal apparatus.
Also, according to the system structure of the conventional portable remote terminal apparatus, even in a block including a clock oscillator such as a PLL synthesizer, a VCO and the like built into the RF/IF control section of the portable remote terminal apparatus, to set the clock oscillator into an oscillating state during the intermittent receiving operation requires the current consumption, which wastes the power of a battery serving as the drive power source of the portable remote terminal apparatus.